Amplitude selective translation circuit



March 17, 1959 P. R. COPE AMPLITUDE SELECTIVE TRANSLATION CIRCUIT Filed Sept. 16, 1955 PIC-3.2 5

QUIESCENT LEVEL VALUE FIXED BY BIAS OF TUBE IO W k INVENTOR. 33 250V PARKER R. COPE A TTORNE YS United States Patent AMPLITUDE SELECTIVE TRANSLATION CIRCUIT Parker R. Cope, Baltimore, Md., assignor to Bendix Aviation Corporation, Towson, Md., a corporation of Delaware Application September 16, 1955, Serial No. 534,699 Claims. (Cl. 179-171) Thisinvention relates to signal translation circuits and more particularly to the type of circuit which is sensitive to the amplitude of the applied signal to provide a gain of one sign to inputs lying within a certain range and to apply a gain of the opposite sign to inputs lying outside of that range.

Such circuits have various uses, one important field being that of the Iso-echo contour indicating apparatus of weather radar systems. position indication (P. P. I.) of storm clouds, with regions of great density being given a contoured configuration for easy identification. I

Various circuits for this purpose have been developed but have retained a complexity which it is desirable to reduce, particularly in viewof the fact that apparatus of this type is usually airborne.

It is an object of this invention to provide an amplitude selective translation circuit which is simple, inexpensive and reliable. P

It is a further object of the invention to provide such a circuit having an output which increases with increasing input amplitude up to a certain level anddecreases with further increases ininput amplitudezabovethis level.

These and other objects and advantages of the invention are realized by a circuit comprising two cathodecoupled vacuum tubes, the first preferably being connected as a cathode follower and being normally biased to or below cut 01f. The tubes are fed in parallel with the input circuit of the second incorporating a voltage divider. The output is taken from the anode circuit of the second tube.

In the drawings:

Fig. 1 is a schematic diagram of a circuit embodying the invention;

Fig. 2 is a graph illustrating the relationship between input and output voltages for the circuit of Fig. 1; and

Fig. 3 is a schematic diagram of a circuit similar to Fig. 1, but incorporating clamping arrangements for clamping the output of the circuit to a reference voltage level.

Referring now more particularly to the drawings, there is shown in Fig. 1 a circuit comprising a pair of triode vacuum tubes and 11 having their cathodes directly coupled by way of a connection 12. The anode of tube 10 is directly connected to the positive terminal 13 of a source of supply voltage and the anode of tube 11 is connected to the same terminal by way of a resistor 14. The cathode connection 12 is connected to ground by way of a resistor 15 and to the terminal 13 through a resistor 16. The control grid of tube 10 is connected to ground through a resistor 17 and a battery 18 in series, the battery 18 representing any source of negative bias voltage for the grid. Input voltage E is applied to the circuit across a pair of terminals 19 and 20, the latter being connected to the control grid of tube 10 and also to the control grid of tube 11 by way of a serial arrangement of a condenser 21 and a resistor 22. The control grid of tube 11 is connected to ground by way of a resistor 23. The output voltage E is taken from the circuit across the 2,878,326 Patented Mar. 17, 1959 ice 1 2 terminals 24 and 25, the latter being connected to the junction of the anode of tube 11 with the resistor 14.

In the operation of the circuit of Fig. l the tube 10 is normally cut off by reason of the negative bias voltage applied by the source 18 and the positive voltage across resistor 15. The input voltage E will normally be a video voltage comprising a train of positive pulses which inthe case of a weather radar system will constitute reflections from cloud formations. As long as the input voltage is not positive enough to drive the tube 10 above cut oil, the tube 11 will amplify the voltage E between its control grid and ground and will yield an output E E will diifer from the input voltage E by a factor determined by the values of resistors 22 and 23. When the voltage E becomes positive enough to raise tube 10 above cut off the current through that tube will flow through resistor 15 and cause a voltage opposing E and will, therefore, reduce the output of tube 11. The rate of the outputreduction is a function of the voltage gain of tube10 and the ratio of E to E. The ratio of the values of resistor 16 to resistor 15 determines the amount of fixed Such systems provide a plan increases in the value of input voltage E the output voltbias on tube 11 and so determines the maximum positivegoing amplitude of the output voltage E The output signal is considered to be composed only of deviations from the quiescent value of the anode to ground potential of tube 11. i

This action is illustrated by the graph of Fig. 2, which shows the output voltage E rising until the input voltage E reaches a value indicated by the line A, which is the point at which tube 10 begins toconduct. For further age E is progressively reduced in magnitude.

If the output voltage E is applied to the intensity electrode of a cathode ray tube the characteristic observed in Fig. 2 will provide a contoured indication on a P. P. I. presentation of a storm cloud formation where the density of the cloud and the associated reflected signal exceedsa certain value represented by the line A on the graph of Fig. 2. This will provide the observer with an indication of the rainfall gradient snfiicient to permit flying a course around the dangerous areas of high turbulence known to be associated with a high gradient.

The circuit of Fig. 3 reproduces that of Fig. l with certain additions. There is shown a tube 30 representing the last video amplifier stage which feeds the circuit of Fig. 1. In this figure the bias source 18 of Fig. 1 has been replaced by a voltage divider comprising a series string of resistors 31, 32 and 33 connected between ground and a source of -250 volts. The control grid of tube 10 is connected to this divider through the resistor 18 and a movable tap 34 on the resistor 32. Across the resistor 18 is connected a diode 35 with its cathode connected to the grid of tube 10. The anode of tube 30 is also connected to the resistor 22 by way of the condenser 21 as in Fig. l. A diode 37 is connected between the junction of condenser 21 and resistor 22 and ground, with the ground connection being made to its anode.

The purpose of the diodes 35 and 37 is to clamp the output voltage E to a fixed reference level. This level is usually fixed as that of the negative excursions of the video voltage applied to the portion of the circuit represented by Fig. 1. While the circuit will operate in the form shown in Fig. l, the presence of serial capacitor couplings causes the output voltage to utilize, :as a reference voltage, the axis of the input voltage. The latter has the characteristic of an alternating voltage having an axis such that the area under the positive excursions equals that under the negative excursions of the pulse train. As the transmitted energy beam illuminates storm areas of differing complexities, so that the duty cycle of the resulting echo wave train changes, the reference level tends also to change. The diodes 35 and 37 thus act as D. C.

, 3 restorers for the input voltage. Adjustment of the tap 34 fixes the inflection level shown generally at A of Fig. 2 at any convenient value required, this level being subject to some operating variation according to the nature and range of the storm and the position of the area of immediate interest.

The voltage values shown in Fig. 3 are by way of example only, and should not be construed as restricting the disclosure.

-What is claimed is:

1. An amplitude selective translation circuit comprising a pair of amplifying stages each comprising a signal responsive variable resistance device, each of said devices comprising an input terminal, an output terminal and a third terminal common to said input and said output, means biasing the first of said devices to an extent such that it does not respond to signal voltages below a se lected level, means directly coupling said third terminals, a common impedance element connected to said third terminals, a source of amplitude varying signal voltage and means coupling signals from said source in'parallel to said input terminals, said coupling means to the input terminal of said second stage comprising an attenuator insensitive to frequency.

2. An amplitude selective translation circuit comprising a pair of amplifying stages each comprising a space discharge tube having at least an anode, a cathode and a control grid, a load impedance element connected to said anode of the second of said stages, means directly connecting said cathodes a common impedance element connected to said cathodes, means biasing said first stage to cut off, a source of amplitude varying signal voltage and means coupling signals from said source in parallel to said control grids, said coupling means providing a greater degree of attenuation to signals coupled to said second stage than to signals coupled to said first stage, said attenuation being substantially independent of frequency over the range of frequencies encompassed by said signals.

3 An amplitude selective translation circuit comprising a pair of space discharge tubes each having at least a cathode, an anode, and a control grid; said cathodes being directly coupled, means connecting said cathodes to a common impedance element, means biasing the first of said tubes to cut off, a source of amplitude varying signal voltage, means coupling said source in parallel to the control grids of said tubes; said coupling means between said source and said second tube providing a greater degree of attenuation than the coupling means bfitween said source and said first tube, and means deriving the output of said circuit from the anode of said second tube, said attenuation being substantially independent of frequency over the range of frequencies encompassed by said signals.

4. An amplitude selective translation circuit comprising a pair of amplifying stages each comprising a space discharge tube having at least an anode, a cathode and a control grid, a load impedance element connected to said anode of the second of said stages, means directly connecting said cathodes, a common impedance element connected to said cathodes, means biasing said first stage to cut off, a source of amplitude varying signal voltage, means coupling signals from said source in parallel to said control grids, and unilaterally conductive means clamping the control grid of said first tube to a reference potential, said coupling means providing a greater degree of attenuati'on to signals coupled to said second stage than to signals coupled to said first stage, said attenuation being substantially independent of frequency over the range of frequencies encompassed by said signals.

5. An amplitude selective translation circuit comprising a pair of amplifying stages each comprising a space discharge tube having at least an anode, a cathode and a control grid, a load impedance element connected to said anode of the second of said stages, means directly connect ing said cathodes, a common impedance element connected to said cathodes, means biasing said first stage to cut ofi, a source of amplitude varying signal voltage, means coupling signals from said source in parallel to said control grids, and unilaterally conductive means clamping the said control grids to a reference potential, said coupling means providing a greater degree of attenuation to signals coupled to said second stage than to signals coupled to said first stage, said attenuation being substantially independent of frequency over the range of frequencies encompassed by said signals.

References Cited in the file of this patent UNITED STATES PATENTS 2,227,050 White et al. Dec. 31, 1940 2,412,279 Miller Dec. 10, 1946 2,732,440 Newman Jan. 24, 1956 2,737,628 Haines Mar. 6-, 1956 

